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Solar pool cover year round in hot climate?

Posted by mudhouse Las Cruces NM zone 8 (My Page) on
Mon, Jun 2, 08 at 2:42

Ive researched solar pool covers here, and I thought most folks used them for the winter, to aid in heating. They usually seemed to be removed in spring, and replaced with a shadecloth.

I thought the purpose of a solar pool cover was to retain heat...a good thing in winter, but a bad thing in summer. However, solar gh (Ron) has been kind enough to mention in a recent thread that his pool cover stays on the outside of his greenhouse (with two layers of shadecloth) in the hot Arizona climate, year round.

After more reading, I found this quote from Stressbaby: "It seems to me that the only reasons for taking off the cover are 1) vents, 2) aesthetics, and 3) wind or wind damage. If the cover transmits 80% of the light, then it's a 20% shade cloth and that could even help with daytime summer cooling. Another thing the cover does is diffuse light... light diffusion prevents foliage burn, improves photosynthesis, and decreases internodal stretch and plant height."

This seems to support Rons practice of keeping his solar pool cover in place year round. (I know Gardenerwantabe keeps his pool cover in place year round, but I don't think he uses his greenhouse in the summer.)

In the same thread, karenrei makes this statement about how a pool cover works:
"The bubbles do what bubbles do: they make it harder to lose heat...In short, things full of tiny air spaces are the best insulators against conductive heat loss."

This is what confuses me. I thought insulating against heat loss on 100 degree summer days would make it hotter inside, and I thought I needed to allow the heat to escape as quickly as possible, to facilitate cooling. I thought my climate was too hot to use a solar pool cover...even on sunny winter days...and definitely during summer.

FYI, my 10x12 greenhouse is glazed with 4mm twinwall polycarbonate. I use my greenhouse year round, including summer days sometimes ranging a bit over 100. My plants (cacti) are fine with occasional 110 days. I have an exhaust fan that capable of 2950 CFM, Aluminet shadecloth, screens on my south wall, and two HAF fans in opposite ends for air movement.

I'd love to know:

1) Can the insulation provided by a solar pool cover aid in cooling my greenhouse in summer, by acting like a 20% shadecloth?

2) If its so good at retaining heat in the winter, why wouldnt it make my greenhouse hotter in the summer by doing the same thing (retaining heat?)

3) Why do you folks remove your pool covers in the summer...just for looks, and/or access to roof vents?

Thanks so much for any help on getting my brain around this issue...I don't want to close the door on any good option.
Sheri


Follow-Up Postings:

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RE: Solar pool cover year round in hot climate?

I can only guess it works like attic insulation.
It keeps heat in in the winter and heat out in the summer.
It depends on which is the hotter or cooler. It keeps the opposite from happening.
I'm sure there is a scientific name for it. But as long as it works I don't need brain overload. LOL
I take mine off to save the cover. The life spans is about 4-5 years but I think they mean seasonal use. Not year round use. Mine has been used 3 winters so far. If I had left it on all year it might be expired by now.


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RE: Solar pool cover year round in hot climate?

1) Can the insulation provided by a solar pool cover aid in cooling my greenhouse in summer, by acting like a 20% shade cloth?
YES

2) If its so good at retaining heat in the winter, why wouldn'tt it make my greenhouse hotter in the summer by doing the same thing (retaining heat?)

Because in winter the GH is closed tight in summer you open the doors and vent it.Cover reduces heat what heat makes it into the GH must be removed. Either with or without a cover your plants will require cooling the cover just reduces the heat load.

3) Why do you folks remove your pool covers in the summer...just for looks, and/or access to roof vents?

I leave mine on year round the one I have is guaranteed for 10 years I also have a shade cloth on mine and I think I will leave it on this winter it will be a small amount of insulation.

As to why others remove their covers probably for different reasons.
I'm lucky my wife is only interested in making the GH efficient for growing plants and so we have no decorations hanging on the walls we both believe pretty is as pretty does
When I read your post a week or so about how you didn't want to use a cover I thought that I was not going to try to change your thinking but now you sound like you are more open to anything that would help so that is why I'm posting to say I think your assessment of how cover works is flawed.
The cover and shade cloth may not keep your panels from deteriorating but it will for sure extend the life of them.

Where you live my guess is regardless what you put on the roof you will need misters to cool in the summer months no amount of insulation will change that.


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RE: Solar pool cover year round in hot climate?

  • Posted by mudhouse Las Cruces NM zone 8 (My Page) on
    Mon, Jun 2, 08 at 21:43

Thanks cactusfreak, I hadnt even considered product lifespan as a reason for removing the pool cover.

You got it, Gardenerwantabe, I posted this thread looking for help in understanding why my assumptions about solar pool covers in hot climates were wrong. (Good to know you found a 10 year pool cover.)

I understand the 20% shade benefit of keeping a pool cover on the roof in summer. But there has to me more to it than that, or folks would just use shade cloth, and in a better density to boot. Now to understand what the solar pool cover does that is different from shade cloth, to see how it can benefit my cooling.

Back to karenrei: "The bubbles...make it harder to lose heat...In short, things full of tiny air spaces are the best insulators against conductive heat loss." So, solar pool covers slow the escape of inside heat from the greenhouse. Right?

That is where I was getting stuck. It seemed wrong that slowing the escape of inside heat in my greenhouse could make it cooler in the summer. Seems like it would make it hotter.

Here is one theory, please tell me if Im wrong. (Heck, tell me if Im right!)

In the winter, the heat comes from inside, created by heaters. The pool cover slows the heat from escaping inside the greenhouse for a longer period before it escapes (just like a 10mm polycarbonate roof would hold the heat in for a longer period than a 4mm poly roof.)

But, in the summer, the heat comes from outside. Does the pool cover slow some of the heat (from the outside sun) from entering the greenhouse in the first place? Is that what Ive been missing?

And, if thats right (the pool cover slows heat from entering in the first place) this must mean a 10mm polycarbonate greenhouse would be cooler in summer than a 4mm polycarbonate greenhouse. Right?

In all the archived threads here about "cooling your greenhouse," I havent seen anyone advise folks to add a solar pool cover in the summer. Only thing I can think of is, a solar pool cover on the roof can help with cooling a small amountbut not nearly as much as the more effective methods of shadecloth, air circulation (exhaust fans, vents) and evaporative cooling (swamp coolers, misters.)

So, Im guessing that a solar pool cover might help cooling to a small degreebut its not as important or effective as the above cooling methodswould you folks agree?


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RE: Solar pool cover year round in hot climate?

So, Im guessing that a solar pool cover might help cooling to a small degreebut its not as important or effective as the above cooling methodswould you folks agree?

YES you still need cooling if you are going to keep plants in it in the summer.

In your case a cover may not be worth the expense but when the cover is on the difference in the way the light comes in is very noticeable.
The cover works like a diffuser.
What the commercial houses do around here in the summer is spray the roof with white wash. Not real pretty but cheap and effective.

I have the west wall of my GH covered from floor to the roof the entire west wall is covered with 2 inch foam insulation.
That makes it warmer in the winter and cooler in the summer.
People worry about what way to sit the GH to get the most sun but mine has no light through the west wall and the plants grow just fine. In fact I sure they do better than if the sun was burning them up all afternoon.
If I lived where you do I would have a 70 or 80 percent shade cloth totally covering the west wall even then you will need cooling like a mister.


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RE: Solar pool cover year round in hot climate?

  • Posted by mudhouse Las Cruces NM zone 8 (My Page) on
    Wed, Jun 4, 08 at 15:37

"If I lived where you do I would have a 70 or 80 percent shade cloth totally covering the west wall even then you will need cooling like a mister."

As we speak, I have more shadecloth on the way. I'll apply it on top of the shadecloth I already have on the west end, to achieve a 70% density. Some of my South African plants like to bake in the afternoon sun, but many find it too intense in the summer, as you said.

Also, I've been using one of those inexpensive wiggly-shaped floor stand personal misters from the box stores, in the center of the greenhouse. My water is too hard to let much mist accumulate on my plants (leaves mineral deposits on the cacti bodies) but even this small mister seems to lower the temps by a few degrees when temps go over 100. Makes it easier for me work in there (although misters sure are hard on hair styles.) ;-)

Now I'll just have to decide if the pool cover would make enough of a difference to justify the expense, in my climate. I appreciate your help Gardenerwantabe.


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RE: Solar pool cover year round in hot climate?

>>My water is too hard to let much mist accumulate on my plants...

If you just have your mister hooked up to the regular water supply, you could get one of those in-line calcium inhibitor filters. They are relatively cheap and depending on how often you mist, you will only need to change them every 8-12 months or so.
Calcium filters are different from water softeners. So make sure you do not confuse the two.

I have one hooked up to my mist system in the GH and it is working great so far. I am going to get another one for my watering hose inside the GH as well.

Here is a link that might be useful: Post about calcium inhibitor filters


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RE: Solar pool cover year round in hot climate?

Wal-Mart has in the camping department a filter that screws on a garden hose to filter water.
They are around 17 dollars
I doubt the pool cover would be worth the money for what you want to do.
Where I live it is a really good deal it saves fuel and diffuses the light to the point that you would just have to see the difference to believe it.
We are going to have a couple days of 90 this week starting tomorrow but after two days it will drop back to normal temps.


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RE: Solar pool cover year round in hot climate?

  • Posted by mudhouse Las Cruces NM zone 8 (My Page) on
    Wed, Jun 4, 08 at 22:51

A filter is a great idea! Thank you both, I'll look into it. I'm new to the whole idea of misters. Most of my plants like low humidity so I thought I could escape learning about it...but when my GH temps went north of 105 I found new motivation to experiment!

Glad to know about the good light diffusion from the solar pool cover, I will keep that in mind.

We're running about 10 higher than normal for this time of year; around 100 most days, but starting tomorrow we should get a break for a while. Now, if someone could just turn off the 40mph wind gusts and turn on the rain spigot, I'd stop whining.


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RE: Solar pool cover year round in hot climate?

Quote SHERI I'd stop whining

I thought woman were always whining
Oh boy now I'm in trouble R.O.F.L


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RE: Solar pool cover year round in hot climate?

  • Posted by mudhouse Las Cruces NM zone 8 (My Page) on
    Thu, Jun 5, 08 at 22:43

Not me...I usually get better results with constant yelling, stomping, and general threats.
;-)


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RE: Solar pool cover year round in hot climate?

And that is the reason she grows cactus instead of leafy plants which can't stand such abuse!!! :-)
Seems the wind has been bad everywhere, even here in Phx .

Ron


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RE: Solar pool cover year round in hot climate?

  • Posted by mudhouse Las Cruces NM zone 8 (My Page) on
    Fri, Jun 6, 08 at 16:29

LOL Ron, exactly right...I do best with plants that have bad attitudes and good defense systems. :-)

Thanks for your post about the solar pool cover, which encouraged me to start this thread. Maybe in another ten years and I'll have my understanding of greenhouses heading in the right direction, with the help of folks online.
Sheri


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RE: Solar pool cover year round in hot climate?

I will get around someday and post pictures of my solar electric for cooling. then you can go spend MORE money. It like fishing, by the time you buy the boat, poles, license and all the other stuff the fish now costs 500 per pound and cheaper to buy it from the store. I figure I have several 500 dollar plants I cold buy for 5.00 each. :-)


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RE: Solar pool cover year round in hot climate?

I am researching the use of solar covers for my greenhouse in the winter. I am curious how people hold the cover on the house as I live in a windy area and am concerned that I will loose it when the wind blows. Are there covers made with gromets to hold down to the concrete foundation? Help.


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